1. Field of the Invention
The invention relates to lubricating grease compositions made from a base oil mixture that consists of a hydrocarbon oil and a perfluoro-polyalkyl ether oil, and a small portion of thickening agent based on a dicarbamide composition, as well as typical additives. The compositions have an especially good noise dampening effect at operating temperatures of from 180.degree. C. to 250.degree. C. This invention also relates to a process for the production of these lubricating grease compositions.
2. Description of Related Art
The development of new lubricating greases must be compatible with the overall further development of technology, which places new and higher requirements on lubricating grease compositions. The known lubricating greases, based on mineral or synthetic oils, no longer measure up to these requirements.
Lubricating greases have application in vehicle technology, materials handling technology, machinery construction, office technology, and in industrial systems and machinery, as well as in the areas of household appliances and consumer electronics.
In roller bearings, lubricating greases assure that a separating, load-transferring film of grease is formed between parts that slide against or roll upon one another. The load-transferring film of grease prevents contact so that no wear occurs. Therefore, the lubricants must satisfy various requirements, among which are:
(a) extreme operating conditions such as very high and very low rotational speeds and loads, PA1 (b) high temperatures that are caused by high rotational speeds and loads or by outside heat sources, PA1 (c) very low temperatures due to low self-heating of the bearing in a cold environment or by intensive heat loss to the cold environment, PA1 (d) special demands of the user on the operating characteristics, for example, low friction, low noise, the demand for extremely long operating times without periodic re-lubrication, PA1 (e) unfavorable ambient conditions and defective sealing of a bearing, and PA1 (f) dynamic effect on the grease, for example, centrifugal force, gravity, vibrations. PA1 A' is --CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, or --CF.sub.2 T, where T is H or Cl, PA1 A" is A' or --CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, or --CF.sub.2 T, wherein T is H or Cl, and PA1 v, w, x, y and z are whole numbers .gtoreq.0.
An important parameter for a long service life of a grease-lubricated bearing in the high temperature range is, aside from the maximum operating temperature according to DIN 51825, the noise aspects of the lubricant. A lubricating grease can, with circulation (rolling over, stretching), cause vibrations ("lubricant noises") in the roller bearing that occur in the medium (300 to 1800 Hz) and high (1800 to 10,000 Hz) frequency bands, as compared with the low frequency band, 50 to 300 Hz. The lubricant noise is superimposed on the noise peaks that result due to shock pulses on the bearing ring when the roller elements roll over hard particles. The evaluation of the noise aspect is performed according to the SKF-Bequiet-Method, which is based on the statistical assessment of the noise surges and their assignment to noise classes BQ1 to BQ4. The noise aspect and the service life of the roller bearings worsen with increasing value of the noise class (H. Werries, E. Paland, FVA-studies on the subject "low-noise lubricating grease" University of Hannover 1994). Thus 100% noise class BQ1 is characterized as very good, and low percentage values exclusively in noise class BQ4 are characterized as very poor noise aspect. The better the noise aspect of a lubricating grease, the less the vibrations of the bearing induced by the grease. This is equivalent to lower loading of the roller bearings and longer service life of the bearing.
A lubricant composition which includes a base oil, such as trimethylolpropane pelargonate, pentaerythritol pelargonate, polyphenyl ether, perfluoroalkyl ether and mixtures thereof, with a thickening agent such as a di- or polycarbamide, is disclosed in U.S. Pat. No. 5,512,188. The dicarbamide can be produced from a diisocyanate and an amine such as octyl amine or aniline. Furthermore, the lubricating grease composition can contain boron nitride or polytetrafluoroethylene (solid lubricants) and additives.
Lubricating greases based on a petroleum oil, or on a synthetic hydrocarbon-based oil, mixed with a perfluoro-polyalkyl ether thickened with an organic or an inorganic thickener, are described in European Patent Application EP-A 0 657 524.
The weight ratio of lubricating oil and perfluoro-polyalkyl ether/thickener lie in the range from 97:3 to 80:20 and the ratio of lubricating oil/perfluoro-polyalkyl ether lies in the range of 95:5 to 60:40. With these lubricating oils and added perfluoro-polyalkyl ether components, the operating time is extended at an operating temperature of 170.degree. C. to 175.degree. C.
Low-noise lubricating greases based on thermally stable polyphenyl ethers, alkylated phenyl ethers, polyolesters and aromatic carboxylic acids, thickened with 5 to 30% by weight of di- and/or polycarbamides are disclosed in U.S. Pat. No. 5,145,591. They can be used at high operating temperatures over 180.degree. C. according to DIN 51825. For operating temperatures greater than 180.degree. C., at present, lubricating greases completely based on perfluoro-polyalkyl ethers, thickened with PTFE, inorganic thickeners, such as bentonites, aerosols or metallic soaps, or metal complex soaps, must be used for operating temperatures above 180.degree. C.
The invention seeks to provide a lubricating grease composition that meets the requirements listed above, is usable in particular under high temperature conditions, and has a very good noise aspect and long operating life, and causes essentially no appearance of wear of the roller bearing.